Water-Gas Shift Catalyst

Abstract

A sintered pelletized catalyst precursor comprising iron oxides, including haematite, and Cr 2 O 3 and optionally one or more of Al 2 O 3 , ZnO, MnO 2 , MgO, and/or CuO, the pelletized catalyst precursor having an iron oxide content of 60 wt % to 95 wt %, when expressed as Fe 2 O 3 , and a Cr(VI) content of less than 0.1 wt %, is physically stable on ignition or when subjected to a reducing gas sufficient to reduce the haematite to magnetite.

What is claimed: 
     
         1 . A pelletized catalyst precursor in the form of a sintered pellet comprising iron oxides, including haematite, and Cr 2 O 3  and optionally one or more of Al 2 O 3 , ZnO, MnO 2 , MgO, and/or CuO, the pelletized catalyst precursor having an iron oxide content of 60 wt % to 95 wt %, when expressed as Fe 2 O 3 , and a Cr(VI) content of less than 0.1 wt %, both relative to the total weight of the pelletized catalyst precursor and wherein the pelletized catalyst precursor (a) exhibits a loss on ignition of less than 3 wt % and/or (b) when subjected to a step comprising subjecting the pelletized catalyst precursor to a reducing gas sufficient to reduce the haematite to magnetite, exhibits a volume shrinkage of less than 1.5% vol and/or retains at least 40% of its mean horizontal crush strength (MHCS). 
     
     
         2 . The pelletized catalyst precursor of  claim 1 , wherein the Cr 2 O 3  or the one or more optional Al 2 O 3 , ZnO, MnO 2 , MgO, or CuO are present in a range of from 1 wt % to 10 wt % relative to the total weight of the pelletized catalyst precursor. 
     
     
         3 . The pelletized catalyst precursor of  claim 1  that contains CuO in a range of from 1 wt % to 10 wt % relative to the total weight of the pelletized catalyst precursor. 
     
     
         4 . The pelletized catalyst precursor of  claim 1  that has been pelletized with a pelleting aid or lubricant. 
     
     
         5 . The pelletized catalyst precursor of  claim 1  wherein essentially all of the iron oxides are present as haematite. 
     
     
         6 . The pelletized catalyst precursor of  claim 1  comprising acicular haematite. 
     
     
         7 . The pelletized catalyst precursor of  claim 1  that exhibits a mean horizontal crush strength (MHCS) of 3 kg F  or more when subjected to the reduction step comprising subjecting the pelletized catalyst precursor to the reducing gas sufficient to reduce the haematite to magnetite. 
     
     
         8 . The pelletized catalyst precursor of  claim 1  consisting of:
 (a) iron oxide in the form of amorphous or acicular haematite, 
 (b) Cr 2 O 3 , and optionally one or more of: 
 (c) Al 2 O 3 , ZnO, MnO 2 , MgO, or CuO and/or 
 (d) a pelleting aid or lubricant; 
 
       the pelletized catalyst precursor having an iron oxide content of 60 wt % to 95 wt % expressed as Fe 2 O 3 , and a Cr(VI) content of less than 0.1 wt %, both relative to the total weight of the pelletized catalyst precursor and wherein the pelletized catalyst precursor (a) exhibits a loss on ignition of less than 3 wt % and (b) when subjected to a reduction step comprising subjecting the pelletized catalyst precursor to a reducing gas sufficient to reduce the haematite to magnetite, exhibits a volume shrinkage of less than 1.5% vol and/or retains at least 40% of its mean horizontal crush strength (MHCS). 
     
     
         9 . The pelletized catalyst precursor of  claim 8  that contains CuO in a range of from 1 wt % to 10 wt % relative to the total weight of the pelletized catalyst precursor. 
     
     
         10 . The pelletized catalyst precursor of  claim 1 , wherein the pelletized catalyst precursor is shaped as a cylinder with a length C and a diameter D, the diameter defining a circumference of the cylinder, and has two or more flutes running along its length, and optionally has domed ends of lengths A and B, wherein (A+B+C)/D is in the range of 0.25 to 1.25 and, when one or both of A and B are present, (A+B)/C is in the range of 0.03 to 0.3. 
     
     
         11 . The pelletized catalyst precursor according to  claim 10 , wherein the pelletized catalyst precursor has domed ends of lengths A and B, wherein (A+B+C)/D is in the range of 0.25 to 1.25 and (A+B)/C is in the range of 0.03 to 0.3. 
     
     
         12 . The pelletized catalyst precursor of  claim 10 , wherein (A+B+C)/D is in the range of from 0.50 to 1.00. 
     
     
         13 . The pelletized catalyst precursor of  claim 10 , wherein (A+B)/C is in the range of from 0.05 to 0.25. 
     
     
         14 . The pelletized catalyst precursor of  claim 10 , wherein the pelletized catalyst precursor has 3 to 12 equally spaced flutes running axially along its length. 
     
     
         15 . The pelletized catalyst precursor of  claim 10 , wherein the flutes are semi-circular, elliptical, or U shaped. 
     
     
         16 . The pelletized catalyst precursor of  claim 10 , having 3, 4 or 5 flutes that each have a width “d” in the range of 0.1D to 0.4D. 
     
     
         17 . The pelletized catalyst precursor of  claim 10 , wherein each of the two or more flutes has a width, which when taken together provide a total flute width that is 35% or less than the circumference of the cylinder. 
     
     
         18 . The pelletized catalyst precursor of  claim 1  prepared by a method comprising the steps of:
 (a) combining a solution comprising one or more iron salts and chromium salts with a solution comprising an alkali metal carbonate to form a suspension having a pH in the range of from 2 to 5 to form a suspension comprising precipitated iron and chromium compounds, 
 (b) adding an alkaline compound to the suspension comprising precipitated iron and chromium compounds to raise its pH to at least 7, 
 (c) separating the precipitated iron and chromium compounds from the suspension, 
 (d) washing the separated precipitated iron and chromium compounds to remove residual alkali metal salts, 
 (e) drying the washed precipitated iron and chromium compounds, and 
 either 
 (f)(i) shaping the dried precipitated iron and chromium compounds by pelleting to form a pellet and then calcining the pellet, or, 
 (ii) calcining the dried precipitated iron and chromium compounds and then shaping the calcined material by pelleting to form a pellet, 
 
       the calcining of step (f)(i) or (f)(ii) being done under inert or non-oxidizing conditions as not to reduce the precipitated iron compounds or oxidize the precipitated chromium compounds. 
     
     
         19 . The pelletized catalyst precursor of  claim 18 , wherein the one or more iron salts comprises iron (II) nitrate, iron (III) nitrate or a mixture thereof. 
     
     
         20 . The pelletized catalyst precursor of  claim 18 , wherein the solution comprising one or more iron salts further comprises a soluble compound of copper, manganese, magnesium, zinc, or aluminum. 
     
     
         21 . The pelletized catalyst precursor of  claim 18 , wherein the combined solution of the iron and chromium salts and the alkali metal carbonate further comprises a particulate metal oxide support material or a particulate metal hydroxide support material. 
     
     
         22 . The pelletized catalyst precursor of  claim 21 , wherein the particulate support material is spherical or comprises support particles having an aspect ratio of at least 2 and an average length within the range of from 500 nm to 1500 nm. 
     
     
         23 . The pelletized catalyst precursor of  claim 18 , wherein the alkali metal carbonate comprises sodium or potassium carbonate, sodium or potassium hydrogen carbonate, or a mixture thereof. 
     
     
         24 . The pelletized catalyst precursor of  claim 18 , wherein the alkaline compound comprises an alkali metal hydroxide. 
     
     
         25 . The pelletized catalyst precursor of  claim 18 , wherein the pH in step (i) is in the range of from 2 to 4. 
     
     
         26 . The pelletized catalyst precursor of  claim 18 , wherein the pH in step (ii) is in the range of from 7 to 10. 
     
     
         27 . The pelletized catalyst precursor of  claim 18 , wherein the washing is performed to reduce the alkali metal content, expressed as alkali metal oxide, of the dried precipitate to 0.25% by weight or less. 
     
     
         28 . The pelletized catalyst precursor of  claim 18 , wherein the drying is performed 150-180° C. in air or non-oxidizing atmosphere so as not to crystallize the precipitated iron compounds. 
     
     
         29 . The method according to  claim 18 , wherein the calcining is performed at a temperature in the range of from 400° C. to 700° C. 
     
     
         30 . The method according to  claim 18 , wherein the non-oxidizing atmosphere is nitrogen or argon, optionally containing 0.1-2% by volume hydrogen. 
     
     
         31 . A pelletized water gas shift catalyst prepared by calcining the pelletized catalyst precursor of  claim 1  under a reducing atmosphere, so as to reduce at least a portion of the haematite to magnetite, the pelletized water gas shift catalyst containing less than 0.1% by weight of Cr(VI), relative to the total weight of the calcined water gas shift catalyst. 
     
     
         32 . The pelletized water gas shift catalyst of  claim 31 , wherein the reducing atmosphere comprises hydrogen and/or carbon monoxide. 
     
     
         33 . The pelletized water gas shift catalyst of  claim 31 , wherein the reducing atmosphere comprises synthesis gas. 
     
     
         34 . The pelletized water gas shift catalyst of  claim 31  that exhibits a mean horizontal crush strength (MHCS) of 4 kg F  or more. 
     
     
         35 . The pelletized water gas shift catalyst of  claim 31 , further containing copper, manganese, and/or zinc formed by reduction of the CuO, MnO 2 , and/or ZnO in the pelletized catalyst precursor. 
     
     
         36 . A process for increasing the hydrogen content of synthesis gas mixture comprising hydrogen, carbon oxides and steam, comprising the step of passing the synthesis gas mixture at an inlet temperature in the range of from 280° C. to 500° C. over the pelletized water-gas shift catalyst according to  claim 31  to form a hydrogen-enriched shifted gas mixture.